Unidirectional helical edge states for all-dielectric topological photonic crystals

The study of one-way edge states of electromagnetic wave based on quantum Hall effect in photonic crystals (PCs) has recently made a great progress. In particular, the pseudo-spin states in topological PCs made of dielectric materials can be realized by breaking pseudo-time-reversal symmetry. We perform a research on the influence of parameters, such as lattice constant, dielectric permittivity of cylinders, radius of the dielectric cylinder and scaling factor of PCs, on the photonic bandgaps of topological PCs. Based on the analysis results, we present a 2D topological PC configuration that supports robust unidirectional helical edge states along zigzag interface between the topologically trivial and nontrivial PCs. With the structure, an operating bandwidth as larger as of 0.0173 (2π c/a) , robust helical edge states with energy-condensed and great nonreciprocity can be achieved by exciting a circularly polarized source. Utilizing this kind of architecture, we construct Z-shaped channel to demonstrate the robustness of helical edge states transport in different cases. The research offers a valid way for realizing unidirectional edge states with robust transport in practicable quantum communication applications.